7 Email Subject Line Mistakes to Avoid

Learning how to craft a winning email subject line is one of the most important things any marketing team can do. The right subject line can help a brand stand out in an otherwise cluttered, crowded inbox.

But mastering the art of subject line writing isn’t easy—it takes time. 

Unfortunately, time isn’t something a lot of marketing teams have, especially during a recession. 

So, how can email marketers (and the brands they represent) get better open rates in as little time as possible?—By avoiding some of the classic mistakes of subject line writing. 

(Full disclaimer, you will NOT be able to avoid all of these mistakes all of the time. Just do the best you can.)

So, without further ado, here are 7 Email Subject Line Mistakes to Avoid.

Email Subject Line Mistake #1 – Forgetting to optimize for mobile 

How often do you check your inbox every day?

And how often do you check that inbox on your mobile device?

These days, more than 61% of email opens come through mobile. That means optimizing for smartphones, tablets, eReaders, etc. isn’t just a good idea—it’s a must-do.  

Subject lines look mighty different on mobile than they do on desktop, so it’s critical to ensure your SLs are as catchy on an iPhone as they are on a MacBook Pro. 

Most email apps will only display the first 35 to 40 characters of a subject line, so put the most compelling part of your message up front. Anything beyond those first 40 or so characters won’t be visible unless your email is opened. 

Email Subject Line Mistake #2 – Being repetitive

Do you regularly use the same words in your subject lines? If so, you’re shooting yourself in the foot.

Subject lines can start to look old mighty quick, and when people start getting bored by your SLs, open rates will slide south. 

To keep things fresh, rotate subject lines with regularity—you don’t need to make dramatic changes on a week-to-week basis, but you should strive to use something decidedly different at least once every four sends. 

  • Include emojis ?
  • Play around with [brackets] and ALL CAPS. 
  • Ask questions (e.g. Tired of unsightly back hair?) or try making bold claims (e.g. Traditional Marketing is DEAD—Here’s Why…).

Email Subject Line Mistake #3 – Talking too much

Don’t use 20 words when two will do.

At Zeta, we’ve seen success using both short and long subject lines, but the shorter ones  (those with less than 30 characters) tend to enjoy higher open rates than those that go 30+. 

The bottom line is, shorter subject lines reflect the changing nature of content consumption. In an era of tweets, TikToks, and ten-second Instagram videos, shorter is better. The less people have to read to get your point (something this article isn’t doing a great job of!) the better your results will be. 

Email Subject Line Mistake #4 – Forgetting to personalize

Everyone knows that dropping a recipient’s first name into a subject line increases the likelihood of getting an open. Yet so many brands forget to do it (including Zeta, if we’re being honest about ourselves!).

But simply including an F_NAME token is just the tip of the iceberg—there are so many other ways to personalize.

Email templates can be personalized to reflect the weather conditions in the locality of the recipient, the recipient’s product purchase history, and so much more. 

The more you know about your recipient, the more you can personalize in a tasteful way. 

And the more you can personalize, the more you can make it feel like a genuine, 1:1 conversation (which people love) instead of a generic message sent to the masses.

Email Subject Line Mistake #5 – Failing to convey urgency or exclusivity

Few things “sell” as well as urgency or exclusivity. So, when it comes to email subject lines, injecting a little “specialness” into your copy is a good idea.

Don’t limit yourself to tired clichés like “limited time offer” and “this weekend only”, but don’t be afraid of them either because they do work.. 

If your email marketing team is struggling to come up with ways to inject a little urgency or exclusivity into subject lines, try incorporating some of these easy concepts into the text:

  • Pre-Sale…
  • Early Bird…
  • Extended Offer…
  • Last Chance…
  • Your First Look…
  • An Offer Just for You…
  • Your Thank You Gift…

Email Subject Line Mistake #6 – Skipping the “From” tag

This is LOW-hanging subject line fruit, but it’s something brands miss time and again.

Who an email is from can influence your open rate to an unimaginable degree. Ideally the “From” tag matches the text included in the subject line, so it’s 100% clear to the recipient who the email is from and why it’s important to open it. (Having said that, the “From” tag doesn’t need to be populated by a real name.)

For example…

  • Nordstrom (GOOD) VS Nordstrom Deals (BETTER)
  • Delta Airlines Service Desk (GOOD) VS Rob at Delta Customer Service (BETTER)
  • Trello (GOOD) VS Taco @ Trello (BETTER)

Email Subject Line Mistake #7 – Rushing

If you think of an email as an advertisement, the subject line is the headline. Therefore, invest in your subject lines like the great David Ogilvy would invest in his headlines…

Spend 20% to 25% of your time on the body of your email, and spend the rest on your subject line.

Will it feel weird the first few times you do it? Absolutely. But avoiding this mistake will do more for your open rates than anything else.

The more time, energy, and money you invest in your subject lines, the more creative and compelling they’ll become.

The more creative and compelling they become, the more your recipients will look forward to receiving emails from your brand. 


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